Steroid hormones act in general to activate transcription from specific genes, but the precise way in which the hormone interacts with the genome is unknown. In order to help clarify how genes and hormones interact, we have begun to study the genetic and endocrine regulation of the process of vitellogenesis, or yolk protein (YP) deposition into the oocytes of Drosophila melanogaster. Three YPs (mol. wt approximately 45,000; 46,000; 47,000) are synthesized in the fat body, secreted into the hemolymph, and sequestered into the developing oocyte. YP synthesis can be induced in isolated abdomens by treatments with either juvenile hormone or 30-hydroxyecdysone. The interaction of genes and hormones will be studied using three methodologies. GENETICS: The structural genes coding for each of the 3 YPs will be sought by examining natural populations for YPs with variant electrophoretic mobilities, and mapping the loci encoding these variations. Female sterile mutations will be induced at the YP structural genes. Regulatory mutants will be sought by screening natural populations for individuals which contain more or less one of the YPs in their hemolymph or ovaries. The mutations will be studied both genetically (by fine mapping) and physiologically. ENDOCRINOLOGY: The hormone which causes the fat body to synthesize YP and the gland which secretes it will be defined by a combination of classical surgical methods and tissue culture studies. The aim is to be able to mimic in tissue culture YP induction in a characterized population of cells. MOLECULAR BIOLOGY: To provide both a reagent for measuring YP gene activities and a molecular access to the YP genes, we will insert DNA fragments complementary to YP mRNA into the bacteriophage by recombinant DNa cloning techniques. The YP cDNA clones will be used to measure the abundance of YP mRNA under different hormonal conditions, and to provide a probe for obtaining YP genomic clones. The structures of the YP genomic clones and the corresponding mRNAs will be investigated. The differences between the YP mutants we propose to produce and wild type will be studied by investigating differences in YP mRNA transcription or translation, and finally by comparing the gene structures both biochemically and by using meiotic genetics.